Recently, for high efficient logistics management and commodity management, the Radio Frequency Identification (RFID) system is popularly applied globally. The RFID system comprises RFID tag having chips, and the reader or reader-writer that can carry out wireless communication with the RFID.
The RFID tag in the RFID system is required to be small as well as reliable in working performance and sufficiently long communication distance. However, the RFID tag is mounted on various objects for use, thus the antenna performance and communication distance are changed because of the influence from the objects on which it is mounted. Especially, when it is mounted on the object with metal surface, the reliability of working performance becomes worse, and the communication distance decreases obviously.
In order to keep the performance of antenna and guarantee stable recognition rate at every position even if the RFID tag is mounted on the metal surface, the invention of the patent document 1 discloses a miniature RFID tag of micro-strip antenna with ground as metal. FIG. 10 illustrates the RFID tag. As illustrated in FIG. 10, the micro-strip patch antenna of the RFID tag includes a power supply part 31 and a radiation part 30 that are mutually connected, and two sides of the radiation part 30 are provided with at least one notch 32.
In consideration of the related technologies of micro-strip antenna, the effective radiating area of the micro-strip antenna has big influence to the transmission gain, and directly influences the communication distance and bandwidth of the communication frequency of RFID tag. If other parameters of the micro-strip antenna are the same, when the effective radiating area becomes bigger, the communication distance of the RFID tag becomes longer and the bandwidth of the communication frequency can also be improved.
However, in prior art, for the micro-strip antenna that works normally, it is necessary to reserve space on the main surface where the radiation surface is mounted to form an impedance match network of the micro-strip antenna and a structure that is used to adjust resonance frequency of the micro-strip antenna. For example, the invention of the patent document 1. Several notches are formed on the radiating part, so as to form the impedance match network and the structure that is used to adjust resonance frequency. Therefore, the effective radiating area of the radiation part in the invention of the patent document 1 is reduced. This shows that considering from improving effective radiating area to improve performance of the micro-strip antenna, there is still a lot to improve the invention of patent document 1.    Patent document 1: CN101728647A